The RyuSae team up was still the most iconic story decision in all of Blue Lock.
Just the impeccable set up, of Shidou starting fights with Rin. Being a menace. Being an extremely talented player, who everyone fears, not just for his spurts of uncontrollable violence, but for his incredible instincts and athleticism.
And Rin hating his fucking guts, because he's a calculating, intellectual player. He has instincts, but he makes decisions based on logic and rationality. They clash because they end up at the same point, but can't explain to the other how they did it, nor can they link up or work together in any meaningful way...
Then Shidou getting locked up because he tries to beat the shit out of Rin, and not put on the starting team, because of his bad behavior.
it is then INSANELY awesome to reveal... well, he won't be playing...with us.
there is someone... outside of Blue Lock...
and who is it, but the main villain of this arc...
AND Rin's personal enemy too, someone he has emotional ties to...
Seriously brilliant, to introduce someone who is the absolute opposite of Rin, and then have him fit so perfectly with his OTHER enemy, his own brother.
It adds a lot of emotional tension, plus it adds a lot of story tension, because holy shit, the guy Blue Lock couldn't handle... is now up against Blue Lock.
I don't know if Blue Lock will ever top how smartly it did U20... I just don't think it can.